Qos For Traffic Directed To The Cpu; Qos Configuration Guidelines And Limitations; Configuring System Classes; Configuring Class Maps - Cisco AP775A - Nexus Converged Network Switch 5010 Configuration Manual

QoS Configuration Guidelines and Limitations

QoS for Traffic Directed to the CPU

The switch automatically applies QoS policies to traffic that is directed to the CPU to ensure that the CPU is
not flooded with packets. Control traffic, such as BPDU frames, is given higher priority to ensure delivery.
QoS Configuration Guidelines and Limitations
Switch resources (such as buffers, virtual output queues, and egress queues) are partitioned based on the
default and user-defined system classes. Cisco NX-OS automatically adjusts the resource allocation to
accommodate the configured system classes.
To maintain optimal switch performance, follow these guidelines when configuring system classes and policies:
• If less than four Ethernet classes are defined, up to two of these classes can be configured as no-drop
• If priority flow control is enabled on an Ethernet interface, pause will never be applied to traffic with a
• All FCoE traffic on an Ethernet interface is mapped to one no-drop system class. By default, this class
• When a Cisco Nexus 2148T Fabric Extender is connected and in use, data traffic should never be marked
Type qos policies can be activated only on Cisco Nexus 5000 Series interfaces and Cisco Nexus 2000
Note
Series Fabric Extender interfaces. Type qos policies on Fabric Extender fabric interfaces or Fabric Extender
fabric EtherChannel interfaces are ineffective, though the Cisco NX-OS CLI does not reject the
configuration.
We recommend that you do not configure type qos policy-maps on Fabric Extender fabric interfaces or
Fabric Extender fabric EtherChannel interfaces to avoid wasting hardware resources.
When configuring EtherChannels, note the following guidelines:
• The service policy configured on an EtherChannel applies to all member interfaces.
• The priority flow control configured on an EtherChannel applies to all member interfaces.

Configuring System Classes

Configuring Class Maps

You can create or modify a class map with the class-map command. The class map is a named object that
represents a class of traffic. In the class map, you specify a set of match criteria for classifying the packets.
You can then reference class maps in policy maps.
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classes. If more than three Ethernet classes are defined, only one of these classes can be configured as
a no-drop class. The default drop class is counted as an Ethernet class.
drop system class. PFC does not apply pause to drop classes and the link-level pause feature is never
enabled on an interface with PFC.
is associated with CoS value 3, although you can configure a different value. If you configure standard
Ethernet traffic to use the same CoS value as FCoE, this traffic is still mapped to the FCoE system class
and the switch will apply priority flow control on the FCoE CoS value.
with a CoS value of 7. CoS 7 is reserved for control traffic transiting the Fabric Extender.
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
QoS for Traffic Directed to the CPU
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